The network must satisfy a number of requirements in order to provide fast data services to users in the downlink direction. For example, first requirement is the data transmitting rate. The data transmitting rate that can be actually supported in the physical layer is preferably high. Second requirement is the data retransmission rate. When some user data has not been successfully transmitted to a user Equipment (UE), the data is preferably retransmitted quickly.
The first requirement is supported by the physical layer and the second requirement is supported by the RLC (Radio Link Control) or MAC (Medium Access Control) layer which is an upper protocol layer. Two functions are required to meet the second requirement. The first function is to quickly determine which data the receiving side has not properly received and the second function is to transmit information, indicating which data the receiving side has not properly received, as quickly as possible to the transmitting side.
In one example, when an E-DCH (Enhanced Dedicated Channel) and a HARQ (Hybrid Auto Repeat Request) function in HSDPA (High Speed Downlink Packet Access) are used, a data block, which began to be transmitted from the transmitting side later than another data block, may successfully arrive at the receiving side earlier than the another data block which began to be transmitted earlier. Thus, the receiving side uses a reordering function in order to use the HARQ function without causing an error according to the data transmission order. Data blocks may arrive at the receiving side in a different order from that intended by the transmitting side unless the reordering function is used.
FIG. 1 illustrates an example where an error occurs according to the data transmission order.
With reference to FIG. 1, let us consider an error that may occur in a reset procedure. First, let us assume that “Y” is an HFN (Hyper Frame Number) value used by a transmitting-side RLC entity during data transmission while “X” is an HFN value used by a receiving-side RLC entity.
In FIG. 1, the transmitting-side RLC entity and the receiving-side RLC entity are represented as TX RLC and RX RLC, respectively.
First, the TX RLC transmits a PDU (Protocol Data Unit) 1 to a lower layer entity after ciphering it with an HFN of “Y” (S10). Before receiving the PDU 1, the RX RLC may initiate a reset procedure to transmit a reset PDU depending on an inner situation (S11). According to a general reset procedure, the TX RLC receives the reset PDU transmitted by the RX RLC and processes the received reset PDU and transmits a reset ACK (Acknowledgment) PDU in response to the reset PDU (S12). Here, an HFNI (Hyper Frame Number Indicator) set to “Z” is included in the reset ACK PDU to be transmitted. As result of reset procedures, RX RLC set transmitting side HFN to “X” and receiving side HFN to “Z”.
The RX RLC may receive the reset ACK PDU, which was transmitted later than the PDU 1 in the HARQ procedure performed at the lower layer entity, before receiving the PDU 1 (S12, S13). If the receiving order of RLC PDUs transmitted from the transmitting side is changed in this manner in the lower entity, the following problems may occur.
The RX RLC will set a receiving side HFN to “Z” after receiving the reset ACK PDU and then, the PDU 1 arrives at the RX RLC after the reset ACK PDU so that the RX RLC will decipher PDU 1 with “Z”. Therefore, the RX RLC cannot properly decode the PDU 1 since the TX RLC ciphered the PDU 1 with the HFN value “Y”.
Meanwhile, it is preferable that reception status information be transmitted quickly in order to increase the data transmitting rate. Even when a receiving-side RLC entity determines which RLC PDU it has failed to receive and immediately transmits its status information to a lower layer entity, the status information will not be able to be quickly transmitted between the receiving and transmitting-side RLC entities in the case where a data transmission delay has occurred at the lower layer entities of both the transmitting and receiving sides or where there is a need to perform reordering. In this case, it is not possible to achieve an increase in the data transmitting rate.